There is ample evidence to suggest that peers are an important influence on adolescent sexual behavior. Yet, very little is known about how often and how much teens communicate with their peers about sex. To date, research in this area has depended upon self-report methods which may be subject to errors in recall, bias, or intentional misreporting of embarrassing material. An additional challenge is that teens use multiple methods to communicate, some of which may tempt them to communicate in riskier ways (e.g., sexting). No studies have directly compared teens' sexual communications across multiple channels. To advance the field, researchers need novel methods to capture these communications as they naturally occur. Real-world, real-time (in vivo) methods have the potential to improve the reliability and validity of sexual communication data and to generate basic science information to inform policies and interventions to reduce adolescent sexual risk. The Overall Aim of this project is to further the study of adolescent peer communications about sex by developing a novel assessment tool to observe and record communications across several different channels. Specifically, we propose to study adolescent peer communications about sex during verbal interactions and text messages using 3 separate tools, all located on a single SmartPhone device. Assessment tools include Ecological Momentary Assessment (EMA) - an in vivo method of self-report, plus two separate methods of in vivo observation, Electronically Activated Recording (EAR) and Random Sampling of Text Messaging (RSTM), that capture spoken language and text messaging, respectively. RSTM is a novel method that will be developed for this project. The first phase of this developmental R21 will involve a series of formative studies designed to develop the integrated assessment tool. These studies will then inform the final phase of this project: a short- term field test. Participants in the field test will carry the assessment device for 16 days during which the EAR will sample brief snippets of sound (including participants' language) from their environment and RSTM will randomly sample a subset of participants' out-going text messages. EAR and RSTM data will be coded along a continuum of sexual content. Participants will also be prompted throughout the day (EMA) to complete brief questionnaires (1-2min) that will provide context to their communications. Data from in vivo monitoring will be used to understand issues related to the feasibility and functionality of the device, to gain a preliminary understanding of the sexual content in adolescents' speech and text messages, and to validate self-report data. We will also examine the dynamic association between sexual communications and sexual beliefs, attitudes and intentions. Data on feasibility, barriers and facilitators to the protocol will be collected, and observational data will be used to advance our understanding of how adolescents communicate with each other about sex. Overall, this study will provide new information about how to effectively assess adolescent communications about sex, and to inform the conduct of larger, longer-term studies on this and related topics.